1. Field of the Invention
The present invention relates to an image capturing apparatus such as a camera array and a method of controlling the same.
2. Description of the Related Art
In recent years, an attempt has been made to implement various functions, which are impossible in a single-eye camera, using images (to be referred to as multi-view images hereinafter) captured at a plurality of viewpoints. For example, there is a refocus process introduced in R. Ng, M. Levoy, et al., “Light Field Photography with a Hand-Held Plenoptic Camera”, Stanford University Computer Science Tech Report CSTR 2005-02, April 2005. The refocus process is image processing of changing the capturing distance (focus) or the depth of field after image capturing and has received a great deal of attention as a technique of solving a problem of image quality such as “out-of-focus”.
A plenoptic method and a camera array method are known as methods of implementing the refocus process. In the plenoptic method, a lens array is arranged in front of an imaging sensor. Light that has become incident on each lens of the lens array is recorded by a plurality of image sensors, thereby divisionally recording light that has become incident on the image capturing device. On the other hand, the camera array method divisionally records light that has become incident on a virtual image capturing device by combining a plurality of camera units.
In either method, the light that has become incident on the image capturing device is divisionally recorded for each direction. Light beams that allow to obtain a desired state are selected from the recorded light beams (light field information) and synthesized, thereby implementing various kinds of image processing represented by the refocus process. Hence, in either method, as the division (to be referred to as parallax hereinafter) of the light incident on the image capturing device becomes finer, the adjustable range can be widened, and the image quality as the processing result improves.
The plenoptic method and the camera array method are different mainly in the following three points.
(1) Output resolution: In the plenoptic method, only an output resolution almost equivalent to that of the microlens array is obtained because of the above-described structure. To the contrary, the camera array method can obtain an output resolution equivalent to the resolution of each camera unit.
(2) Fineness of parallax: A camera of the plenoptic method (to be referred to as a plenoptic camera hereinafter) obtains light field information of small parallax divided by the lenses included in the lens array. However, the parallax of a camera of the camera array method (to be referred to as a camera array hereinafter) depends on the distance (base-line length) between the camera units, and it is therefore difficult to obtain a small parallax. Hence, in the camera array method, the camera units are arranged as densely as possible to minimize the base-line length.
(3) Power consumption: The plenoptic camera adds a lens array in front of the imaging sensor of a general digital camera and has a power consumption equal to that of the digital camera of the base. To the contrary, the camera array includes a number of camera units, and its power consumption increases in accordance with the number of camera units.
Concerning the problem of power consumption of the camera array, a technique of cutting power supply to some components to reduce the power consumption has been proposed in the field of security cameras. There exists, for example, a technique of controlling power supply to the camera or an illumination device in accordance with a person detection result in a specific area.
However, the camera array has not only the problem of power consumption but also the problem of thermal noise generated by the densely arranged camera units. In the camera array, the camera units need to be arranged densely due to the above-described reason. Each camera unit is affected by heat from the camera units arranged in the periphery, and the thermal noise increases.
It is the image quality of the camera unit (to be referred to as a center camera unit hereinafter) arranged near the center of the camera array that most affects the quality of an image obtained by the camera array. However, since many camera units are arranged around the center camera unit, the thermal noise of the center camera unit tends to increase. In other words, it is important in the camera array to obtain light field information as much as possible while suppressing the thermal noise.